The present invention relates to materials handling systems and more particularly to material handling systems for bulk materials.
Bulk materials such as grains, ores, coal, sand, gravel, cement, wood chips and plastic pellets are often transported or moved from storage in bulk material handling systems in whole or in part by gravity induced flow. The rate of such gravity induced flow may vary widely due to relatively minor differences in particular batches of bulk material which may be transported or moved from storage or due to changes which may occur over time in the same batch of material.
These bulk materials are made up of particles which are in contact with one another but which have voids between them which are filled with a gas, usually air. Essentially they are two-phase, solid-gas systems, and their flowability may be difficult to predict even under ideal conditions. In actual practice, they may often contain additional liquid or solid materials such as moisture, oils, clays, soils and organic contaminants. Aside from such additional materials, the flowability of the bulk material may also be affected by variations in the physical, chemical and physiochemical changes in the bulk material itself. Because such particle-gas systems are often compressible their flowability may be affected by changes in density. Other physical conditions which might affect flowability include variations in particle size, size distribution and shape. Chemical factors would include changes in surface character due to oxidation or other chemical reactions. Physiochemical factors would include changes in adhesion and cohesion which might be induced by changes in ambient temperature. Variations in flowability can cause materials to accumulate in chutes, bunkers, silos and transfer points of material handling systems. Substantial accumulations can result in complete blockage and extensive material handling system outages. These outages are particularly troublesome in coal fired electric generating plants, where interruption of coal supply due to material handling problems can cause loss of generating capacity.
It is, therefore, an object of the present invention to provide a means for easily and inexpensively predicting and preventing material handing problems resulting from variations in flowability conditions.